All-fiber wavelength-selective filters are the key components in fiber communication systems, those based on fiber couplers incorporated with Bragg gratings are compact, low insertion loss and low cost. In this paper, the filter based on 244 nm ultraviolet-written Bragg grating in hydrogen-loaded conventional 2×2 3-dB fused coupler is reported. It exists an optimized position and appropriate length of grating to obtain high reflectivity from drop port. The filter with maximum reflectivity about 20 dB, bandwidth larger than 1 nm is obtained. The results are qualitatively analyzed with supermode theory. In order to obtain high drop efficiency, the position of the grating and the speed of the step motor should be carefully controlled.